Media Polarization
The media plays a key role in this film as we watch as they search to identify who Nick Dunne is. Is he a faithful husband searching for his husband, or the prime suspect in her disappearance and possible murder? The media polarizes him in order to create the story that will sell to everyone watching. The film shows the reality of the type of polarization the media can create in our day and age.
Dishonesty
Dishonesty is a primary theme of this film. We see Amy create a disappearance that has the media stirring up a hornets nest with all accusations beginning to point towards Nick as the prime suspect. Amy creates this entire ploy in order to get revenge on her husband who she tells us he has taken everything from her which she believes in a type of murder he's committed upon her.
Manipulation
Manipulation is seen throughout the entire film. Amy manipulates Nick, Desi and he media. Nick has manipulated Amy. All of it has turned a seemingly fine privileged life into one that is upended by Amy's false disappearance which ends in her return and yet another manipulation of Nick in order for him to stay quiet about what she's done.